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Snapchat is still vulnerable to hackers -- and that could mean bad news for iPhone users. Jamie Sanchez, a security researcher who first discovered the flaw in the popular picture messaging app, said Snapchat opens the iPhone up to denial-of-service attacks that can cause the device to freeze and crash.

“Snapchat uses security tokens for authentication,” he wrote in a blog post. “Security tokens are used to prove one's identity electronically, in place of a password, to prove that the customer is who they claim to be, so they don't have to exchange the original password that may be captured by attackers.”

As Sanchez explained it, a token is created any time you make a request to Snapchat to update your contact list, add someone, send a snap, etc. The “request token” is based on your password and a timestamp, among other things. The problem is that the tokens don’t expire like they should.

Android Not Immune

“I've been using for the attack one token create almost one month ago. So, I'm able to use a custom script I've created to send snaps to a list of users from several computers at the same time,” Sanchez said. “That could let an attacker send spam to the 4.6 million leaked account list in less then one hour.”

But that’s not the only problem. According to Sanchez, any attacker could just send all the snaps to one user only as a denial of service attack. That could crash the iPhone and force a restart to free the phone from the attacker’s grip. Apparently, the attack only crashes on iPhones -- not Android-powered devices. But Sanchez said the attack does slow down Android phones to the point where it’s impossible to use the device until the attack is over.

Sanchez does have some good news: If you have friends-only settings, and the attacker is not in your friend list, it shouldn't affect you.

Irresponsible Disclosure

We caught up with Chester Wisniewski, a senior security advisor at Sophos, to get his take on the Snapchat issue. He told us he’s not surprised there was another flaw discovered in Snapchat seeing as the company’s attitude toward security seems to be more reactive than proactive. But Wisniewski takes exception to how Sanchez handled the disclosure.

“Yes, it is never fair to publicly disclose flaws without giving the company the opportunity to respond,” Wisniewski said. “It is imperative that zero-day vulnerabilities in applications are handled carefully and respectfully if you want to consider yourself a researcher rather than an anarchist. Public disclosure without notification leads to innocent people being harmed and generally does not achieve anything positive for the user nor the security community.”

As Wisniewski sees it, the fix for Snapchat should be reasonably simple -- but it may require an update to its phone applications, which may take a bit of time to test and get approved by the application markets. He advised Snapchat users to check their privacy settings and not accept Snaps from users who are not their friends and not to blindly accept new friend requests.